LINEAR-MOTOR STATOR WITH INTEGRAL LINE REACTOR
A linear-motor stator assembly comprising a stator and an integral line reactor in one housing. The reactor has inductor coils which are connected in series with the stator windings to compensate for unequal inductances in the stator phases and balance the polyphase currents into the stator.
The invention relates generally to polyphase linear motors and more particularly to line reactors unitarily housed with linear-motor stators.
Linear induction motors and other linear motors are often configured as polyphase motors, usually with three phases. Because of magnetic end effects and winding layouts, the inductances of the stator windings typically differ from phase to phase. The stator phases should be excited by currents nearly equal in magnitude so that an optimal traveling magnetic flux wave is generated. The current imbalance in stators resulting from unequal phase inductances is solved in two main ways. One solution is to drive the stator coils with a current-regulated amplifier, but current-regulated drives are expensive. Another way stator inductances are balanced is with inductive reactors. Inductor coils in the reactors are connected in series with the stator windings to balance the net inductances of the phases so that the stator can be driven by a more common variable-frequency drive (VFD). Because the reactors are separate units external to the stators, they must be packaged with and electrically connected to the stator. The packaging and the cabling can be difficult in harsh environments, such as those requiring NEMA 4X or IP67 washdown ratings.
SUMMARYOne version of a linear-motor stator assembly embodying features of the invention comprises a stator and a reactor. The stator includes a stator core portion having a first end and an opposite second end defining the length of the stator core portion and an outer face having a plurality of pole faces separated by a plurality of stator coil slots opening onto the outer face between the first and second ends. A plurality of sets of stator coils reside in the stator coil slots and are connected to form polyphase stator windings propagating a magnetic flux wave along the length of the stator portion through the pole faces. The reactor includes a reactor core portion abutting the stator core portion and having an outer face with a plurality of inductor coil slots opening onto the outer face. A plurality of inductor coils reside in the inductor coil slots. Each of the inductor coils is connected electrically in series with one or another of the sets of stator coils.
Another version of such a linear-motor stator assembly comprises a core that includes a first outer face and a second outer face. The first outer face extends in length from a first end to a second end and has a plurality of pole faces separated by a plurality of stator coil slots opening onto the first outer face between the first and second ends. The second outer face has a plurality of inductor coil slots opening onto the second outer face. Three sets of stator coils reside in the stator coil slots and are connected to form three-phase stator windings propagating a magnetic flux wave through the pole faces along the length of the first outer face. A plurality of inductor coils reside in the inductor coil slots. Each of the inductor coils is connected electrically in series with one or another of the sets of stator coils.
In another aspect, a linear-motor system comprises a housing, a stator having three stator windings housed in the housing, a reactor having inductors housed in the housing adjacent to the stator, and a three-phase variable-frequency drive. The inductors are electrically connected between the three-phase variable-frequency drive and one or more of the three stator windings to balance the currents in the three stator windings.
A stator assembly embodying features of the invention is shown in
Pairs of slots 28, 28′ open onto the bottom outer face 17 of the core 12 to receive inductor coils 30A-C—three, in this example. There are more stator coil slots 18 than inductor coil slots 28, 28′. A core piece 32 between each pair of inductor coil slots 28, 28′ extends through the center of each inductor coil and forms a high permeability core for the coil. A steel plate 34 separated from the inductors' core pieces 32 and the bottom outer face 17 of the core 12 by a gap 36 serves as a magnetic shunt completing the inductors' magnetic circuits. The plate 34 can also serve as a mounting plate for the stator assembly 10. When electrically connected to the stator coils 22, the inductor coils 30A-C can compensate for differences in the reactances of the stator coils. Thus, the induction coils are equivalent to line reactors.
In
The electrical wiring of the stator portion of a linear-motor system with the reactor inductors connected between the stator windings and a VFD is shown schematically in
Instead of the back-to-back configuration of the stator assemblies of
The invention has been described in detail by reference to a few example versions. But other versions are possible. For example, the system could be a polyphase system of more than three phases. The use of the terms “integral” or “unitary” with respect to the stator and the reactor means that they are joined and enclosed together in a single housing. The unitary stator and reactor can share a common monolithic (solid or laminated) core or can have separate cores closely spaced from each other. One is not external to the other's housing.
Claims
1. A linear-motor stator assembly comprising:
- a stator including: a stator core portion having: a first end and an opposite second end defining the length of the stator core portion; an outer face having a plurality of pole faces separated by a plurality of stator coil slots opening onto the outer face between the first and second ends; a plurality of sets of stator coils residing in the stator coil slots and connected to form polyphase stator windings propagating a magnetic flux wave along the length of the stator portion through the pole faces;
- a reactor including: a reactor core portion abutting the stator core portion and having: an outer face having a plurality of inductor coil slots opening onto the outer face; a plurality of inductor coils residing in the inductor coil slots, wherein each of the inductor coils is connected electrically in series with one or another of the sets of stator coils.
2. A linear-motor stator assembly as in claim 1 wherein the stator includes three sets of stator coils connected to form three-phase stator windings and wherein the reactor includes three inductor coils and wherein one of the inductor coils is connected electrically in series with one of the three sets of stator coils and the other two of the inductor coils are connected electrically in series with each other and with another one of the sets of stator coils.
3. A linear-motor stator assembly as in claim 2 wherein the at least two inductor coils are connected electrically with the three sets of stator coils to compensate for unequal reactances in the three sets of stator coils.
4. A linear-motor stator assembly as in claim 1 further comprising a steel plate facing the outer face of the reactor core portion to provide a magnetic shunt for the reactor and to serve as a mounting plate for the linear-motor stator assembly.
5. A linear-motor assembly as in claim 1 wherein the stator core portion and the reactor core portion are complementary portions of a monolithic core whose obverse face is the outer face of the stator core portion and whose reverse face is the outer face of the reactor core portion.
6. A linear-motor stator assembly as in claim 1 wherein the stator core portion and the reactor core portion are separate cores magnetically isolated from each other and encapsulated together into a unitary structure.
7. A linear-motor stator assembly as in claim 1 wherein the reactor core portion abuts the first end of the stator core portion and the outer face of the stator core portion and the outer face of the reactor core portion face in the same direction.
8. A linear-motor stator assembly as in claim 1 wherein there are more stator coil slots than inductor coil slots.
9. A linear-motor stator assembly as in claim 1 further comprising an array of electrically conductive rollers arranged in parallel along the length of the stator core portion across a small gap to serve as rotors rotated by the magnetic flux wave and forming linear induction motors with the stator.
10. A linear-motor stator assembly as in claim 1 further comprising an array of rollers arranged in parallel along the length of the stator core portion across a small gap and including permanent magnets, wherein the rollers serve as rotors rotated by the magnetic flux wave and form linear synchronous motors with the stator.
11. A linear-motor stator assembly comprising:
- a core including: a first outer face extending in length from a first end to a second end and having a plurality of pole faces separated by a plurality of stator coil slots opening onto the first outer face between the first and second ends; a second outer face having a plurality of inductor coil slots opening onto the second outer face;
- three sets of stator coils residing in the stator coil slots and connected to form three-phase stator windings propagating a magnetic flux wave through the pole faces along the length of the first outer face;
- a plurality of inductor coils residing in the inductor coil slots, wherein each of the inductor coils is connected electrically in series with one or another of the sets of stator coils.
12. A linear-motor stator as in claim 11 wherein the first outer face is an obverse face of the core and the second outer face is a reverse face of the core.
13. A linear-motor stator as in claim 11 wherein the first outer face and the second outer face face in the same direction.
14. A linear-motor stator assembly as in claim 11 further comprising a steel plate facing the second outer face to provide a magnetic shunt for the inductor coils and to serve as a mounting plate for the linear-motor stator assembly.
15. A linear-motor system comprising:
- a housing;
- a stator having three stator windings housed in the housing;
- a reactor having inductors housed in the housing adjacent to the stator;
- a three-phase variable-frequency drive;
- wherein the inductors are electrically connected between the three-phase variable-frequency drive and one or more of the three stator windings to balance the currents in the three stator windings.
16. A linear-motor system as in claim 15 further comprising an array of electrically conductive rollers arranged in parallel across a small gap from the stator to serve as rotors rotated by a magnetic flux wave and forming linear induction motors with the stator.
17. A linear-motor system as in claim 15 further comprising an array of rollers arranged in parallel across a small gap from the stator and including permanent magnets, wherein the rollers serve as rotors rotated by a magnetic flux wave produced by the stator and form linear synchronous motors with the stator.
Type: Application
Filed: Mar 10, 2016
Publication Date: Sep 14, 2017
Patent Grant number: 10003246
Inventor: Bryant G. Ragan (Metairie, LA)
Application Number: 15/066,064